connection problem

now i have windows 7 . i lose all others cars for 3sec after every 30sec in server , i can drive but i dont see others for 3sec after every 30sec. firewall settings are right too. Dont know where the problem is. help please.

ok i found problem, if i set rfactor priority to high, then i got these lags, but i cant play without high priority, then i have some stupid lags, dont matter with what quality i play, still got these lags. With vista i played with high quality but now cant.
These are my pc info: processorintel core 2 duo E7300 2,66GHz, 4gb ram, 1gb radoen hd 6850 card